Training devices with electric motors for training of muscles are known in the art. For example training devices are known, wherein a computing unit supplies a frequency converter with setpoint values for the amperage and the frequency of the current of a three-phase AC motor provided for generating torque. The computing unit is supplied with the output signal of a position sensor measuring the position of a motor-driven crank which acts as a training element. By means of stored tables containing all the relevant machine-specific parameters, the computing unit calculates the values of the amperage and frequency of the motor current required for a desired course of the torque over position based on the position value of the motor-driven crank. These devices lack high accuracy necessary for a smooth training over high torque ranges.
Other training devices known in the art having a three-phase AC motor for generating torque measure two values: the speed of rotation of the motor is measured by a frequency-analogue rate sensor and the torque output is measured by a force sensor. The speed of rotation measured is used for controlling the frequency and the torque measured is used for controlling the motor current. The concept of this training device thus comprises two sensors and two interconnected control loops and its implementation therefore involves relatively high design complexity. Measuring the force by a sensor further involves potential problems such as the effects of temperature, drift as well as malfunctions resulting from vibrations or impacts.
Moreover, other training devices are known in the art having a three-phase AC motor being associated with an angle-of-rotation sensor whose measured signal is supplied to both a frequency converter and a control unit. Within these devices, the control unit provides a setpoint value for the torque to be generated by the motor and the frequency converter controls the torque by a closed control loop (comprising of the frequency converter, the AC motor and the sensor attached to the motor with its feedback to the frequency converter) using the principle of field-oriented control, also known as vector control. However, these devices have several disadvantages. First, the angle-of-rotation sensor has to detect multiple turns of the motor, as there is a reduction gear in front: This either makes the sensor a relatively complex part or additional calculations are needed to obtain the absolute position of the training element. Secondly, there is no direct information about what is happening at a motor shaft. Backlash of the gearbox and other effects after the motor shaft that might even be safety critical can hardly be detected by this design.
Further, e.g., Halabeya (High Performance Electrical Drive System for a Biomechanical Text and Rehabilitation Equipment, 2000) describes a “regular” DTC (direct torque controlled) scheme for controlling of induction motor drive within a training device used for physical rehabilitation. Such a DTC control scheme compares a reference torque and a reference flux with actual values of torque and flux. Based on this comparison control signals are produced by using a hysteresis control method. However, the reference flux is used as exclusive control value within this device in order to achieve a fast torque response time. Thus, the dosage of the torque at the motor shaft is not sufficiently precise and, further, negative effects of a high magnetization may occur. Both result in an undesirable high stiffness of the drive system, especially if the motor operates in the second or forth quadrant (i.e. “as a brake”) and at low speeds. Moreover, Halabeya teaches the usage of an angular sensor mounted at the load shaft with its signal feed back to the frequency converter. The safety measure consists of four switches which are mounted near the load shaft and signal the lever bar has reached its upper or lower range of motion limits. Consequently, the device described by Halabeya does not allow detecting dangerous events like a broken link between the angular sensor and the load shaft or a malfunction within the frequency converter. Thus, the training device as described by Halabeya does not provide sufficient safeness.
There is therefore an unmet need for an improved training apparatus enabling a highly accurate responsive training resistance, safeness and quick torque response time of the motor of the training apparatus.
According to the invention this need is settled by a training apparatus as it is defined by the features of independent claim 1, by a training arrangement as defined by the features of independent claim 11, and by a method for operating the training arrangement as it is defined by the features of independent claim 13. Preferred embodiments are subject of the dependent claims.
In particular, the invention deals with a training apparatus comprising a training element for an exercising person, an AC motor and a frequency converter being arranged to control the AC motor, wherein the frequency converter comprises measuring means being arranged to measure a voltage and a current of the AC motor and calculation means being arranged to calculate a magnetic state of the AC motor using the measured voltage, the measured current, a reference torque and a reference flux in order to generate a torque of the AC motor. Such a calculation can be used within a DTC control scheme for control of the AC motor. The training apparatus further comprises a control unit having a machine control module being arranged to calculate the reference flux and the reference torque using an intended overall torque, wherein the machine control module is connected to the frequency converter and arranged to transmit the reference flux and the reference torque to the frequency converter.
In use, the training element is subject to a force exerted by the exercising person of the training apparatus during training and which may be as a non-limiting example a crank. The training element may have many different forms, such as that of a bowshaped grip, a handle or the like or of one or two pedals or a cable that is connected to the shaft by a cable winch. The scope of the present invention shall not be limited to a crank, but comprises all conceivable kinds of variants of a training element to which a person can apply muscle force. These likewise include, among other things, training elements which do not carry out a rotational but a translator motion which latter will then be mechanically converted into the rotation of a motor shaft. In this case, the terms used here for angle of rotation, speed of rotation and torque shall correspond to the terms for translatory shift or translatory speed, or force, respectively. During such exercise, the force that needs to be applied by the motor depends on a great number of parameters, including mechanical friction and inertia and of course the type of exercise the exercising person wants to perform. For this reason, the control unit calculates the reference torque and reference flux during the exercise in order to provide continuously or discontinuously the frequency converter with the calculated reference torque and reference flux. The inventive arrangement of the training apparatus allows for the provision of advantageous effects such as a quick torque response time of the AC motor in combination with a comparably precise control of the torque generated by the motor with less effort. The torque response time is particularly important at the reversal points of the exercise motion, as often changes from one direction to the other are desirable from a training perspective. Advantageously, the reference flux is adjusted as a function of the absolute amount of torque needed at an output shaft of the AC motor. This highly improves the training experience at lower torques and allows dosing the torque very precisely over a wide range and is also beneficial for the reduction of energy consumption and thus lowers the cooling requirements and allows building systems with no forced cooling but only convection cooling. This allows avoiding the noise generated by a blower.
Preferably, the machine control module splits the intended overall torque into a torque component and a flux component within the control unit, and calculates the reference flux and the reference torque based on the torque component and the flux component using a characteristic diagram. This calculation of the reference torque and reference flux within the training apparatus is particularly useful for the reduction of stiffness of the AC motor and for precise control of the torque generated by the AC motor.
Preferably, the machine control module of the control unit is arranged to calculate the intended overall torque based on a predefined training resistance provided to the control unit and a correction factor. The calculation of the intended overall torque based on the predefined training resistance and the correction factor is useful for compensating friction and mechanical inertia of the training apparatus whereby the exercises are convenient to the exercising person. The predefined training resistance can change dependent on a training lever's state of motion including its position, speed and acceleration, the predefined training resistance can change dependent on each repetition of the exercises, the predefined training resistance can change dependent on elapsed time within the exercises or the predefined training resistance can change dependent on the direction of the exercises.
As used herein, the term “predefined training resistance” relates to a weight or a level of difficulty predefined at the training apparatus or predefined otherwise as described herein below (e.g. at a web interface, at a user interface) by the exercising person wherein each effort is performed against a specific opposing force generated by resistance (i.e. resistance to being pushed, squeezed, stretched or bent). Such a predefined training resistance is used to develop the strength and size of skeletal muscles.
Preferably, the machine control module comprises a hybrid controller in order to generate the reference torque and the reference flux to the frequency converter. The hybrid controller operates before the calculation of the reference torque and reference flux takes place.
The use of a hybrid controller within the training apparatus enables a combination of multiple controllers which are switchable on the basis of discrete states, such as a state where only the torque is set and a state where the position is controlled instead as well as states that relate to safety functions. For safety reasons, the maximum speed of the motor is limited so that the training element cannot snap back with the maximum possible speed in case the exercise person releases it or slips off. Also, for safety reasons it may be expedient to limit the maximum torque of the AC motor in order to avoid the risk of overstress and the danger to sustain injuries.
Preferably, the machine control module comprises a cascade control arrangement in order to generate the reference torque and the reference flux to the frequency converter.
As used herein, the term “cascade control arrangement” relates to a control model for controlling motor drives, such as the AC motor, wherein an inner control circuit for a speed of rotation (ω) and for an outer control circuit for the position (phi) is provided. Limits of phi and ω can be integrated as saturation functions within this circuit or be integrated in the frequency converter. Such a cascade control arrangement is useful for improving a reliability of safety critical measure within the training apparatus. The detailed mode of implementing this cascade control arrangement into the training apparatus is known in the art.
Preferably, the calculation means of the frequency converter comprises mathematical models for calculating the magnetic state of the AC motor. Such mathematical models are useful for the determination of the magnetic state of the AC motor and, thus, contribute to a precise control of the AC motor.
As used herein, the term “mathematical model” relates to a model in order to describe the training apparatus. In this context, mathematical models can take many forms, including but not limited to dynamical systems, statistical models or differential equations, tables or combinations thereof. These and other types of models can overlap, with a given model involving a variety of abstract structures and can be implemented to describe the training apparatus.
Preferably, the calculation means of the frequency converter comprises mathematical models for calculating rotational speed of the AC motor and temperature of the AC motor. The calculation of the rotational speed of the AC motor and the temperature of the AC motor enables a precise control of the reference torque and reference flux within the training apparatus. Further, in order to keep track of the temperature of the AC motor without using a temperature sensor, a thermal model is used to approximate the motor temperature.
Preferably, the training apparatus comprises an angular position sensor being connected to the training element, wherein the angular position sensor is arranged to sense a position of the training element and to transmit the sensed position to the control unit and wherein the control unit is arranged to adjust the reference torque and the reference flux using the sensed position.
The angular position sensor mounted to the training element, for example comprising a lever arm. The angular position sensor provides feedback of the actual motion of the lever arm to the control unit, which adjusts the reference torque and the reference flux according to the value of the angle position sensor, the rotation speed calculated by the frequency converter and a specific dataset of exercising person. Preferably, with respect to the safeness of the training apparatus, it is envisaged not to feedback the signal of the angular position sensor mounted at a lever shaft to the frequency converter, but to the higher-ranking control unit. Thus, it is possible to detect dangerous events like a broken link between the angular position sensor and the load shaft of the AC motor or a malfunction within the frequency converter.
For an efficient training and for safety reasons it is important to limit the possible range of motion of the exercising person. In order to achieve this, the control unit can vary the torque depending on the angle of the lever arm, which is measured by the angular position sensor at the lever arm, so that if a given angle is crossed, the torque increases as if there was a mechanical stop. The increasing torque might as well increase as a function of the further angular movement, so that, for instance, a mechanical spring can be simulated. In order to prevent the lever from recoiling, the additional force may depend on the direction of movement and set to zero for the direction the spring would normally expand to.
Preferably, the control unit comprises a communication module being arranged to transmit training data comprising the predefined training resistance and to obtain training data. As used herein, the term “training data” relates to data which are required before starting a training comprising personal and body-specific data, apparatus settings such as position of the exercising person, positions of fixations of the apparatus, and a training schedule comprising training goals, training methods, frequency of the training, number and order of training apparatus, frequencies of training heats, training weights. Likewise, the term “training data” relates to data which are recorded during a training comprising frequency of an exercise and exerted weight, data of the sensor signal of the angular position sensor and degree of accomplishing the training goals. Such a communication module is useful for transmitting the training data from the training apparatus, for example, to a remote database server, such as a central database server, and further for receiving training data of an exercising person.
Preferably, the communication module is arranged to be connected to a database in order to store training data in the database and to obtain training data from the database. This embodiment is, for example, useful in order to transmit a unique identification to the database which has been provided by the exercising person identifying at the training apparatus using an identification system, e.g. smart-card, contactless smart-card, finger-print detection, user identification number, personal identification number (PIN) system, barcode device, magnetic card or wireless device comprising radio frequency identification device (RFID) and bluetooth device. The database can be implemented on a local database server, on a remote database server, such as a central database server, or in the training apparatus itself. The term “database server” as used herein relates to a computer program that provides database services to other devices, modules or apparatus. Implementing the database on the training apparatus itself makes it possible to use the machine even if the network connection fails temporarily and thus improves the reliability and failure safety of the machine.
Preferably, the communication module is arranged to be connected to a network and to transmit and receive training data via the network. The communication module is useful for transmitting and receiving data over a network connection. As a non limiting example, the communication module transmits the results of training at the training apparatus to a remote database and receives data about the training of an exercising person who wants to exercise at the training apparatus.
In a further aspect of the invention, a training arrangement comprises a training apparatus as described above and a database and a web interface, wherein the database is connected to the web interface and to the communication module of the control unit of the training apparatus, wherein the web interface and the database are arranged to store or manipulate training data via the web interface. This training arrangement is useful for providing an interactive way to support the exercise person to meet his or her training goals.
Preferably, the database of the training arrangement is connected to the web interface via the World Wide Web. As used herein, the term “World Wide Web” is to be understood as a computer network consisting of a collection of formatted documents that offer data, such as training data, through the hypertext transfer protocol accessed via the Internet. The documents are formatted in a markup language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means it is possible to jump from one document to another by clicking on hot spots. There are several applications, like web browsers, that enable to access the World Wide Web. Accordingly, the World Wide Web is an efficient tool for exchanging data, such as training data within the training arrangement or within the training apparatus.
In another further aspect of the invention, a training arrangement comprises a training apparatus and a database and a web interface, wherein the database is arranged to be connected with the web interface and with the training apparatus.
In another further aspect of the invention, a method for operating the training arrangement comprises the steps of transmitting training data comprising the predefined training resistance to the database, manipulating the transmitted training data via the web interface, and transmitting the manipulated training data to the control unit of the training apparatus of the training arrangement.
As used herein, the term “user interface” relates to a module by which people interact with the training apparatus. Such a user interface can include hardware (physical) and software (logical) components. User interfaces exist for various devices, modules or apparatus, and provide a means of input, for example, allowing the exercising person to manipulate such devices, modules or apparatus, and/or output, for example, allowing the system to indicate the effects of the exercising persons' manipulation.
Preferably, transmitting training data within the method according to the invention comprises transmitting a predefined training resistance from the web interface to the database.
Preferably, the method further comprises the step of synchronizing data being stored in the database with a central database server, wherein the data comprises transmitted training data, manipulated training data, training data comprising a predefined training resistance.
In another further aspect of the invention, a method for operating the training arrangement according to the invention comprises the steps of transmitting training data comprising a predefined training resistance from a user interface to a database, manipulating the transmitted training data by using the web interface, and transmitting the manipulated training data to a control unit of a training apparatus of the training arrangement according to the invention.
As used herein, the term “synchronization” is to be understood within the field of computer science and refers to the need to keep multiple copies of a set of data, such as training data coherent with one another. A synchronization of data, such as training data, between the database or the remote database server such as the central database server and the web interface may be carried out either continuously or discontinuously. The synchronization of all kind of data, such as training data comprising manipulated training data, transmitted training data and training data comprising a predefined training resistance is envisaged within the method according to the invention. Thus, the synchronization of training data can occur in different ways such as between the database and the remote database server such as the central database server via World Wide Web, or between the database and the web interface being arranged to store data, or between the user interface being arranged to store data and the database and/or the remote database server such as the central database server.
Preferably, training programs are classical exercises with predefined resistance and a predefined number of repetitions and sets, or a “pyramid” training where the resistance will start at a low level, increase with the first half of repetitions and decrease with the second half of the repetitions. Also, a program for measuring the maximum strength of the exercising person is envisaged within the present invention. For this, the torque at the lever arm can be increased with the angle of the lever arm, similar to a mechanical spring, and the maximum angle the exercising person reaches is proportional to her maximum strength. As an alternative method, a lever arm can be controlled in a way to keep a fixed position by using a closed control loop. The amount of torque needed for the controller to keep this fixed position is a measure for the force the exercising person exerts on the training lever. This way, a maximum force can be measured in an isometric way. After the exercise has been finished, a set of data describing all training results is generated. Within this set of data, information about the completed repetitions, sets, weights as well as records of the sensor data are stored and transmitted over the network connection to a remote database. In turn, this database can be accessed via a database server where the gathered data and other analyses, based on this data, can be viewed by the exercising person through a website. Also, adjustments to the saved variables, e.g. the training plan, can be accomplished over the database or the central database server and will be synchronized over the network connection of the training apparatus, so that those adjustments are available the next time as soon as the exercising person identifies at the training apparatus.